Order Book and DOM (Depth of Market) Explained
What is an order book?
An order book is the live list of resting limit orders for an instrument: everyone willing to buy below the current price (bids) and everyone willing to sell above it (asks or offers). The depth of market (DOM) is the same information laid out as a ladder of prices with the quantity waiting at each.
Every trade you see on a chart starts here. A market order consumes resting orders on the other side of the book. When enough orders at one price are used up, price moves to the next level. Reading the order book is reading the queue that price has to get through.
Parts of the depth of market
Best bid and best ask
The best bid is the highest price a buyer is currently offering; the best ask is the lowest price a seller will accept. Together they make the top of the book.
Spread
The bid-ask spread is the gap between them. In liquid contracts such as NIFTY futures it is usually one tick most of the session. A widening spread signals thinner liquidity, common around news, the open and the last minutes of expiry.
Depth levels
Below the best bid and above the best ask are more price levels with their own queues. Many Indian brokers show five levels of depth; some feeds offer 20 or more. Total bid quantity and total ask quantity summarise the visible book.
Order count
NSE depth also shows how many separate orders make up each level. A 2,000-lot level built from 300 orders is different from one built from 2 orders, and the second is more likely to be pulled.
How market orders and limit orders interact
A limit order adds liquidity and waits in the book. A market order takes liquidity and executes immediately against the best opposite price. The aggressor is always the market order, which is why order flow tools measure buying and selling by who crossed the spread.
If 500 lots rest at the best ask and a 700-lot market buy arrives, the first 500 fill there and the remaining 200 fill at the next ask level. Price ticks up because the queue at the old level was exhausted. This is the micro-mechanics behind every candle.
How to read the order book
Stacked bids or offers
Large resting orders at one level are sometimes called walls. A big bid wall below price may slow a decline, and a big offer wall above may slow a rally, as long as it stays.
Pulling and stacking
Watch what happens as price approaches a wall. If quantity increases as price nears it (stacking), the participant seems committed. If it disappears before being touched (pulling), the wall was not real interest.
Refreshing orders and icebergs
Sometimes a level keeps getting hit but the visible size keeps reappearing. That points to an iceberg or a participant refilling the order. In the footprint this shows as heavy volume at one price with little progress, which is a form of absorption.
Imbalance in the book
Total bid quantity much larger than total ask quantity looks like buying pressure, but it is only intent. It changes in milliseconds and should be read together with executed trades, not alone.
Spoofing and why the DOM can mislead
Spoofing means placing large orders with no intention of letting them fill, to make others think there is demand or supply. Spoofing is illegal on NSE and SEBI acts against it, but large orders that are pulled before execution still appear.
Because resting orders can vanish, many traders give more weight to executed volume, shown in the footprint chart, than to the visible book. The book shows what might happen; the tape and footprint show what did happen.
DOM vs footprint vs time and sales
| Tool | Shows | Strength | Weakness |
|---|---|---|---|
| Order book / DOM | Resting limit orders | Where liquidity waits | Orders can be pulled |
| Time and sales | Each executed trade | Exact prints | Hard to read fast |
| Footprint | Executed bid/ask volume per price per bar | Summarises aggression and absorption | Does not show unexecuted orders |
| Cumulative delta | Running buy-minus-sell aggression | Trend of pressure | Ignores passive side |
The tools complement each other. See cumulative delta (CVD) for the running version of aggression.
Worked example: NIFTY futures depth
Illustration only; numbers are plausible, not historical.
NIFTY futures trade at 24,600. The book shows a large bid of several hundred lots at 24,580 and normal sizes elsewhere. As price slides to 24,590 the 24,580 bid grows larger. Price touches 24,580, a few thousand contracts trade there, and the bid refreshes rather than disappearing.
The footprint for that bar shows heavy selling at the bid at 24,580 and a long lower wick. A trader would read this as a passive buyer defending the level. If instead the 24,580 bid had vanished when price came within two ticks, the reading would be that the wall was never real support.
Liquidity, slippage and order types
Depth is not only an analysis tool; it directly affects your fills. If you send a market order larger than the quantity at the best price, part of it fills at worse prices. That difference is slippage.
Thin options strikes
Far OTM options and stock options often have wide spreads and few lots at each level. A market order there can fill several ticks away from the last traded price. Limit orders reduce this, at the cost of sometimes not being filled.
Stop-loss orders
A stop-loss market order becomes a market order when triggered, so it fills at whatever the book offers. In a fast move through a thin book, slippage on stops can be large. A stop-limit order controls price but may not fill at all. Knowing the normal depth of your contract helps you choose.
Why liquidity pools form
Many traders place stops just beyond obvious highs and lows. That creates clusters of resting orders, the liquidity that larger participants may need to fill size. It is one reason price often trades briefly through obvious levels before reversing.
Common mistakes reading depth of market
- Trusting visible size. Big resting orders are not commitments.
- Reading the book in isolation. Without executed volume you cannot tell intent from action.
- Using index depth. Use the futures or the stock itself; the index has no book.
- Ignoring the time of day. Depth is thin around 9:15 and in the last minutes of expiry, so walls mean less.
- Over-trading every flicker. The book changes many times a second; focus on behaviour at your prepared levels.
Seeing it on the TradingMarble chart
The TradingMarble chart focuses on executed order flow: the footprint shows bid and ask volume at each price, along with delta and levels, so you can study how price reacted where resting liquidity was tested. See the features page for what each chart includes.
Order book checklist
- Know the normal spread and depth for the contract.
- Note large resting orders near your levels.
- Watch whether they stack, hold, refresh or get pulled as price arrives.
- Confirm with executed volume in the footprint.
- Ignore depth in illiquid moments such as the open and the expiry close.
- Combine with key levels and liquidity instead of trading the book alone.
The order book and DOM show where liquidity sits; they do not predict direction. F&O trading carries a high risk of loss, so use market depth as one input among many.
Frequently asked questions
What is depth of market in trading?
Depth of market (DOM) is a display of the resting buy and sell limit orders at each price level near the current price. It shows the best bid, best ask, the quantity waiting at each level and often the number of orders. It tells you how much liquidity price has to get through to move.
How do you read an order book?
Start with the best bid, best ask and spread. Then look for unusually large resting orders near important levels and watch how they behave as price approaches: do they hold, refresh, grow or get pulled? Confirm what you see with executed volume, because resting orders can be cancelled.
What is spoofing in the order book?
Spoofing is placing large orders you do not intend to let fill, to create a false impression of demand or supply, and cancelling them before they execute. It is prohibited by SEBI and exchanges. It is one reason traders give more weight to executed volume than to visible depth.
Is a high total bid quantity bullish?
Not by itself. Total bid quantity only shows intent at that moment, and orders can be modified or cancelled quickly. It becomes useful when executed trades agree, for example sellers hitting the bid repeatedly without moving price. Treat book imbalance as context, not a forecast.
What is the difference between DOM and footprint?
The DOM shows resting limit orders that have not traded yet. The footprint shows volume that actually traded at each price, split into bid and ask. The DOM tells you where liquidity is waiting; the footprint tells you how aggressive traders interacted with it.